1. Technical Field
The present disclosure relates to an improved ambient light sensing system and method, for use in a sensor such as a single photon avalanche diode (SPAD).
2. Discussion of the Related Art
A SPAD is based on a p-n junction device biased beyond its breakdown region. The high reverse bias voltage generates a sufficient magnitude of electric field such that a single charge carrier introduced into the depletion layer of the device can cause a self-sustaining avalanche via impact ionization. The avalanche is quenched, either actively or passively to allow the device to be “reset” to detect further photons. The initiating charge carrier can be photo-electrically generated by means of a single incident photon striking the high field region. It is this feature which gives rise to the name ‘Single Photon Avalanche Diode’. This single photon detection mode of operation is often referred to as ‘Geiger Mode’.
A SPAD array is used in mobile phones, communication devices and computers for a number of different sensor functions. These functions include ranging functions, ambient light sensing and a variety of other functions.
In respect of ambient light sensing there are a number of different types of light conditions which must be dealt with. For example, the different types of light may include daylight, fluorescent light, incandescent light etc.
Each different type of light emits at a different frequency spectrum and the
response of the sensor, such as a SPAD, is different at different incident frequency spectra. This results in an ambient light response which varies depending on the type of light being compensated for. Ideally the response, from a user point of view, should be the same for the same levels of light (LUX) irrespective of the frequency or wavelength spectrum.
In addition, where a sensor is being used for multiple functions, such as range finding and ambient light sensing the sensor may operate in both the optical and infrared spectra. As a result, the sensor may detect ambient light in still further frequency ranges which again give rise to different responses.